1. Field of the Invention
The invention is directed to an improved brake device for vehicle brake systems and more particularly to an improved brake device used in electrohydraulic anti-lock brake system.
2. Description of the Prior Art
Brake devices of the type with which this invention is concerned are used in electrohydraulic anti-lock brake systems or brake systems without mechanical coupling between the brake actuating pedal and the master cylinder. The primary parameters for regulating these electrical brake systems are the operating pressures occurring in the brake circuits, which are detected by pressure sensors of the brake device and converted into electrical measured values. The electronic control unit evaluates the measured values together with other sensor signals and generates appropriate trigger signals for the brake assembly.
In a known brake device of this type (German Patent Disclosure DE 197 11 366 A1), a plurality of pressure sensors are connected via a circuit substrate to a plug assembly secured to a printed circuit board. The electrical connection with the electronic control unit is established via a plug, connected to a connecting cable that leads to the electronic control unit, and this plug has to be plugged onto the plug assembly.
In another known pressure conducting device (U.S. Pat. No. 4,536,820) of the type defined at the outset, a pressure sensor for pressure measurement and an electronic control unit disposed with spacing from it are provided and have opposed contact faces. An electrical connection between the pressure sensor and the electronic control unit is established by means of spring contact pins. To this end, sleeves of the spring contact pins reach through a spacer body disposed between the pressure sensor and the electronic control unit. The sleeves are connected to the spacer body in pressure-tight, electrically insulated, and displaceable fashion. While the spring contact pins are braced with spring force on the face on the contact faces of the pressure sensor, spring contacts disposed on the contact faces of the electronic control unit engage the sleeves of the spring contact pins. The pressure sensor, the spacer body with the spring contact pins and the electronic control unit are housed in a housing fitted over them and the housing is secured to the pressure-conducting device.
The assembly of these components is relatively complicated: First, the pressure sensor must be connected in pressure-tight, nondisplaceable fashion to the pressure-conducting device. Then the spacer body, with the sleeves of the spring contact pins secured in it, must be mounted on the pressure-conducting device. Then the housing is joined to the pressure-conducting device. Finally, the electronic control unit has to be installed in the housing. Automatic assembly of the pressure-conducting device is therefore possible only with difficulty.
The brake device according to the invention has the advantage that fully automatic assembly of the brake device is possible, in which once the housing containing the electronic control unit has been fitted over the at least one pressure sensor, the electrical connection is established automatically between the pressure sensor and the electronic control unit. The housing is secured to a hydraulic block of the brake device, in which the at least one pressure sensor is also inserted, so that the spring contact pins are braced with a defined contact pressure on the contact faces of the pressure sensor and the electronic control unit and assure secure transmission of signals and data.
In an advantageous embodiment of the invention, the spring contact pins have a sleeve with a helical compression spring located inside it and have at least one pin, which is axially displaceable in the sleeve and is urged by the helical compression spring in the expulsion direction out of the sleeve. The spring contact pins can be embodied in various ways. In a simple version, the contact pin on the one hand, and the entirely or partly closed one end of the sleeve on the other form the contact parts that contact the contact faces of the pressure sensor and the electronic control unit. The compression spring is braced between the pin and the end of the sleeve. In another embodiment, two pins are provided, with each protrude from the sleeve at one end thereof. The helical compression spring received in the sleeve is braced between the two pins and presses one pin against a contact face of the electronic control unit. In all cases, a stop is formed on each pin and cooperates with a respective counterpart stop in the sleeve, so that the pin, in the absence of counterpressure before the final assembly, cannot be expelled from the sleeve.
In a preferred embodiment of the invention, the pressure sensor has a cup-shaped measurement cell and a flange receiving the measurement cell, which flange protrudes with a central protrusion into the measurement cell and with a central peg into a bore embodied in a hydraulic block, and which flange is provided with a central through bore that penetrates the protrusion and the peg. By means of the protrusion protruding into the measurement cell, the hollow space in the measurement cell is reduced to the minimum required, which assures that relatively large proportions of residual air cannot become separated in the measurement gap and adulterate the pressure measurement. The flange, as a simple turned part, is easy to make and assures the connection of the measurement cell with the interior of the hydraulic block; in a further embodiment of the invention, after the placement of a seal the flange is calked in the hydraulic block, after the placement of a seal in a plunge cut embodied on the peg. The cup-shaped measurement cell, on its cup edge resting on the flange, is welded to the flange. Both the calking and the welding can be done simply and economically in an automated process.
The electrical connection of the pressure sensor to the contact faces toward the sensor that are acted upon by the spring contact pins is done, in accordance with advantageous embodiments of the invention, via gold bonding wires to a spray-coated stamped grid surrounding the pressure sensor, on which grid a printed circuit board which in turn carries the contact faces is disposed. The printed circuit board is soldered to the stamped grid, and the stamped grid is provided with ground contact by means of at least one forklike flat plug, embodied integrally on the stamped grid, that protrudes into an annular groove machined coaxially into the flange, and there the plug makes electrical contact for the flanks and/or the bottom of the groove. The spray-coated stamped grid is received on the face end in the annular groove and is fixed to the flange by wedging in of one edge of the groove.
In an advantageous embodiment of the invention, the electronic control unit has an electronics box, which is disposed on the face end of the housing remote from the pressure sensor, and it also has a stamped grid, held in front of it in the housing; this stamped grid, on its underside remote from the electronics box, carries the contact faces that are assigned to the control unit.